Prophylactic or therapeutic agent for diabetic maculopathy

ABSTRACT

A prophylactic or therapeutic agent for diabeticmaculopathy, which can be administered for a long time and exhibits efficacy in a mechanism different from that of existing medicines. The invention relates to a prophylactic or therapeutic agent for diabetic maculopathy, comprising, as an active ingredient, a compound represented by the general formula: 
     
       
         
         
             
             
         
       
     
     wherein X represents a halogen or a hydrogen atom, R 1  and R 2  concurrently or differently represent a hydrogen atom or an optionally substituted C1 to C6 alkyl group, or R 1  and R 2 , together with a nitrogen atom bound thereto and optionally another nitrogen atom or an oxygen atom, are combined to form a 5- to 6-membered heterocycle. Preferably, the compound is (2S,4S)-6-fluoro-2′,5′-dioxospiro chroman-4,4′-imidazolidine]-2-carboxamide. The invention also provides a model animal with diabetic maculopathy produced by subjecting a diabetic animal to intraocular ischemia/reperfusion to express edema in a retinal visual cell layer or in a macula lutea.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/587,320, filed May 10, 2007, which is the National Phase ofInternational Application No. PCT/JP2005/001187 having an internationalfiling date of Jan. 28, 2005, and claims the benefit of JapaneseApplication 2004-022547, filed Jan. 30, 2004, the entireties of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a new use of a hydantoin derivative, inparticular, (2S,4S)-6-fluoro-2′,5′-dioxospiro[chroman-4,4′-imidazolidine]-2-carboxamide, as a pharmaceuticalpreparation.

2. Description of the Related Art

The number of patients with diabetes mellitus as a life style-relateddisease is increasing, and in a survey on diabetes mellitus in 2002conducted by the Ministry of Health, Labor and Welfare, the number ofpatients with diabetes mellitus in Japan is estimated to be 7.4millions. In a recent epidemiological study on 913 cases ofnon-insulin-dependent diabetes mellitus, about 8% (about 600,000patients) of patients with diabetes mellitus are reported to havemaculopathy. It is estimated that as the number of patients withdiabetes mellitus increases, the number of patients with diabeticmaculopathy also increases.

Diabetic maculopathy, together with diabetic retinopathy, is consideredto be important as one of the retinal diseases inpatients with diabetesmellitus. Diabetic maculopathy is classified into macular edema,ischemic maculopathy, retinal pigment epitheliopathy and maculartraction. The object of diabetic retinopathy therapy is to preventblindness (loss of visual acuity), while the object of diabeticmaculopathy therapy is to prevent and ameliorate deterioration of visualacuity. Macula lutea are significantly different in form from retinas soas to attain high central visual acuity (sharpest and high visualacuity), and have a special structure (absent from an inner plexiformlayer and an inner nuclear layer) with extremely fewer tissues otherthan visual cells. Accordingly, the clinically problematic deteriorationof visual acuity is due to maculopathy. A development ofphotocoagulation and vitrectomy made it possible to almost preventblindness attributable to retinopathy, but is not satisfactory formaculopathy, so a therapy that is different from retinopathy therapy isneeded for maculopathy. This is also important in light of the treatmentof many patients having maculopathy only without having retinopathy.Especially, a recent increase in pan-photocoagulation for diabeticretinopathy is estimated to worsen macular edema in diabeticmaculopathy, to cause further deterioration of visual acuity.Accordingly, the main point of therapy is shifting toward improvement ofquality of life (QOL) of patients by maintaining and improving visualacuity.

Macular edema caused by breakage of a blood-retinal barrier in a retinalvascular endothelial cell or a retinal pigment epithelial cell accountsfor about 90% of maculopathy and is a major cause for deterioration ofvisual acuity in maculopathy. This deterioration of visual acuity doesnot lead to blindness, but causes extreme deterioration of visual acuityreferred to as social blindness making usual living difficult. On onehand, the average life span increases due to the advancement of medicaltechnology, and thus, such a deterioration of visual acuity is a seriousproblem that cannot be neglected in consideration of QOL. Major therapyconducted for preventing or ameliorating deterioration of visual acuityincludes photocoagulation, vitrectomy and chemotherapy. Under thepresent circumstances, photocoagulation and vitrectomy are examined fortheir effectiveness in clinical studies, and the effectiveness andsafety for macular edema have still not been established. There arecases where complications of neovascular glaucoma and worsening edemaoccur, and thus, there is an earnest desire for the advent of aneffective and safe chemotherapy. In the present chemotherapy, steroidsand carbonate dehydratase inhibitors with anti-inflammatory action asmajor efficacy are used in symptomatic therapy, but their effectivenessis not established and their administration over a long period of timeleads to the occurrence of side effects, and thus, the continuous usethereof in chronic diseases such as diabetes mellitus is not desirableunder the present circumstance.

(2S,4S)-6-Fluoro-2′,5′-dioxospiro[chroman-4,4′-imidazolidine]-2-carboxamide(hereinafter, referred to as SNK-860) found by the present applicant wasdeveloped as a compound which has a strong inhibitory activity on aldosereductase and is highly safe even in administration for a long time, andclinical test thereof as a therapeutic agent for diabetic neuropathy isadvancing worldwide at present.

With respect to hydantoin derivatives including SNK-860, the use thereoffor diabetic neuropathy is described in JP-A 61-200991 (1986), the usethereof for diseases in circulatory organs in JP-A 04-173791 (1992), theuse thereof for various diseases accompanying aging in JP-A 06-135968(1994), the use thereof for simple diabetic retinopathy in JP-A07-242547 (1995), and the use thereof for diabetic keratopathy in JP-A08-231549 (1996). However, the effectiveness of the hydantoinderivatives for diabetic maculopathy has not been reported.

As described above, establishing an effective and highly safe therapyfor treating diabetic maculopathy is strongly desired in the medicalfield. Under the present circumstances, the advent of a highly safechemotherapy enabling administration over a long time period is stronglydesired because of the safety problems associated with treatment byopthalmologic operation. However, heretofore, there has been no modelfor evaluating experimental diabetic maculopathy, which is important forthe development of such therapeutic agents, and the establishment of anexperimental model for development of pharmaceutical preparations is anurgent task.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the drawbacksassociated with the prior art as described above, and an object of thepresent invention is to provide a prophylactic or therapeutic agent fortreating diabetic maculopathy, which can be administered over a longperiod of time which and exhibits efficacy in a mechanism different fromthat of existing medicines, as well as an experimental animal modelwhich can be used in the evaluation of medicines for diabeticmaculopathy.

The present inventors first sought to establish an experimental animalmodel for diabetic maculopathy. That is, simplicidentata such as ratshave no macula lutea, and there is no report on edema at a site outsideof a retina such as a visual cell layer, that is, at a sitecorresponding to macula lutea, and whether its severeness is increasedor decreased by diabetes mellitus is not reported either. Accordingly,the present inventors studied its pathologic condition using an animal,and as a result we found that when a diabetic rat was allowed to be inan intraocular ischemic state and then subjected to reperfusion, edemawas expressed on a visual cell layer. In this experimental model, it issuggested that an increase in oxidation stress, such as excessiveproduction of free radicals occurring in the eye by ischemia andreperfusion, promotes vascular permeability by breaking an innerblood-retinal barrier (barrier regulating the transfer of a substancefrom a retinal blood vessel to the outside of the blood vessel) and anouter blood-retinal barrier (barrier regulating the transfer of asubstance from a choroid to retina). Accordingly, it is estimated thatthe edema was expressed by this promotion of vascular permeability inaddition to the promotion of retinal vascular permeability by diabetesmellitus. The present model thus expressing edema in the visual celllayer has an onset mechanism very similar to that of macular edema inhuman diabetic maculopathy and can be said to be a model suitable forthe evaluation of diabetic maculopathy.

The present inventors also examined whether or not edema was expressedin a macula lutea in a diabetic monkey by using an evaluation systemestablished in rats. As a result, it was confirmed that edema isobserved in a macular central fovea participating most in central visualacuity. This can be said to further evidence that the edema-expressingmodel established in a rat is suitable in evaluation of diabeticmaculopathy.

When the present inventors used the above-mentioned experimental modelto evaluate SNK-860, the inventors discovered that SNK-860 is effectivefor edema in a retinal visual cell layer having a central role inmaintaining visual acuity or for edema in a macula lutea (particularlymacular central fovea). By conducting further clinical evaluations, thepresent inventors discovered that the compound is not only effective fortreating edema in a macula lutea, but also exhibits an effect ofimproving visual acuity. That is, the present invention relates to aprophylactic or therapeutic agent for treating diabetic maculopathy,which comprises, as an active ingredient, a hydantoin derivativerepresented by the following general formula, preferably(2S,4S)-6-fluoro-2′,5′-dioxospiro[chroman-4,4′-imidazolidine]-2-carboxamide (SNK-860)

(In the formula, X represents a halogen or a hydrogen atom, R¹ and R²concurrently or differently represent a hydrogen atom or an optionallysubstituted C1 to C6 alkyl group, or R¹ and R², together with a nitrogenatom bound thereto and optionally another nitrogen atom or an oxygenatom, are combined to form a 5- to 6-membered heterocycle, and thehalogen represented by X is preferably fluorine, and the C1 to C6 alkylgroup is preferably a methyl group.)

Examples of the diabetic maculopathy include macular edema and retinalpigment epitheliopathy. Examples of the diabetic macular edema includelocal macular edema and diffuse macular edema. The prophylactic ortherapeutic agent for diabetic maculopathy according to the presentinvention is preferably in the form of an oral agent.

The present invention also relates to an experimental animal model withdiabetic maculopathy, which uses an animal such as simplicidentata orprimates other than humans. This is an animal model with diabeticmaculopathy that is produced by subjecting a diabetic animal tointraocular ischemia/reperfusion to express edema in a retinal visualcell layer or in a macula lutea (particularly in macular central fovea).As the animal with diabetes mellitus, it is possible to use not onlyanimals having diabetes mellitus induced for example by administering apharmacological agent such as streptozotocin or alloxan into a rat(normal rat) or a monkey (normal monkey), but also animals withhereditary diabetes mellitus.

Further, the present invention encompasses a method of evaluating apharmacological agent for diabetic maculopathy, which comprises usingthe model animal described above. That is, the method of the presentinvention is a method of evaluating the effectiveness of apharmacological agent on edema, which comprises administering apharmacological agent to be evaluated into the model animal andmeasuring the thickness of a retinal visual cell layer or the thicknessand/or volume of a macula lutea.

The present invention provides not only a therapeutic agent for diabeticmaculopathy, which can be administered over a long period of time, butalso an experimental animal model that is needed in order to conductresearch to discover a therapeutic agent for diabetic maculopathy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the ratio of the thickness of a retinal visual cell layer(ratio (%) of the thickness of a visual cell layer in anischemic/re-perfused eye/the thickness of a visual cell layer in anuntreated eye in the same individual) in Efficacy Pharmacological TestExample 1. In FIG. 1, the asterisk indicates that there is a significantdifference with a risk factor of 5%.

FIG. 2 shows the ratio of the thickness of a retina visual cell layer(ratio (%) of the thickness of a visual cell layer in anischemic/re-perfused eye/the thickness of a visual cell layer in anuntreated eye in the same individual) in Efficacy Pharmacological TestExample 2. In FIG. 2, the asterisk indicates that there is a significantdifference with a risk factor of 5%.

FIG. 3 shows a change in the minimum thickness, average thickness andaverage volume of macular central fovea in an ischemic/re-perfused eyein Efficacy Pharmacological Test Example 3. In FIG. 3, the asteriskindicates that there is a significant difference with a risk factor of5%.

FIG. 4 shows the thickness of a macula lutea in a macular central fovea(diameter: 1 rum) and in the center of the central fovea before andafter administration in Efficacy Pharmacological Test Example 4.

FIG. 5 shows a change in the thickness of a macula lutea in individualeyes (upper graph, in the center of a central fovea; lower graph, in thecentral fovea in the diameter range of 1 mm) before and afteradministration in Efficacy Pharmacological Test Example 4. A number inthe example indicates identification number of the case, and alphabetsOS and OD refer to left and right eyes, respectively.

FIG. 6 shows corrected visual acuity before and after administration inEfficacy Pharmacological Test Example 4.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention is described in more detail.

Hydantoin derivatives (particularly SNK-860) can be orally administeredfor example as tablets, capsules, powder, granules, liquid or syrup orparenterally as an injection and suppositories, which were formed byusual pharmaceutical manufacturing techniques. Pharmaceuticallyacceptable excipients in pharmaceutical manufacturing, for examplestarch, lactose, refined white sugar, glucose, crystalline cellulose,carboxy cellulose, carboxymethyl cellulose, carboxyethyl cellulose,calcium phosphate, magnesium stearate and gum arabic can be used in thesolid preparation, and if necessary a lubricant, a binder, adisintegrating agent, a coating agent, a coloring agent etc. can beincorporated into the solid preparation. In the liquid preparation, astabilizer, a solubilizer, a suspending agent, an emulsifying agent, abuffer agent, a preservative etc. can be used. The dose varies dependingon symptoms, age, administration method, preparation form etc., butpreferably the compound described above is administered usually in therange of 1 to 200 mg, preferably 1 to 100 mg, into an adult all at onceor in divided portions per day for consecutive days.

In the model animals with diabetic maculopathy according to the presentinvention, animals with diabetes mellitus by treating normal animalswith a pharmacological agent such as streptozotocin (STZ), or alloxan oranimals with hereditary diabetes mellitus, can be used as diabeticanimals. As the type of the animals, simplicidentata such as rats,nonhuman primates such as monkeys, duplicidentata such as rabbits, andcarnivorous animals such as canines can be used.

When the simplicidentata, duplicidentata or carnivorous animals thatinherently do not have macula lutea are used, edema is expressed in aretinal visual cell layer and the thickness of the retinal visual celllayer can be used in evaluation. In the nonhuman primates, on the otherhand, there are usually macula lutea, so edema is expressed in a maculalutea and the thickness and/or volume of the macula lutea is used inevaluation. The thickness etc. of the macula lutea are evaluatedpreferably in the site of macular central fovea. Intraocularischemia/reperfusion treatment can be easily carried out by stopping aretinal blood stream by increasing the intraocular pressure and thenrelieving the intraocular pressure to allow reperfusion. The thicknessof the retinal visual cell layer or the macula lutea variessignificantly depending on individuals, so a treated eye and untreatedeye are set preferably in the same individual by subjecting only one eyeto intraocular ischemia/reperfusion treatment. By so doing, the relativeevaluation of “thickness of a treated eye/thickness of an untreated eye”can be carried out on the basis of the untreated eye in each animal.

A pharmacological agent to be examined is administered into the modelanimal with diabetic maculopathy according to the present invention andthen evaluated for the effectiveness of the pharmacological agent foredema as described above, whereby the effectiveness of thepharmacological agent for diabetic maculopathy can be evaluated. Themethod of administering the pharmacological agent is not particularlylimited, and administration of the pharmacological agent is also carriedout after intraocular ischemia/reperfusion treatment thereby clarifyingthe therapeutic effect.

EXAMPLES Efficacy Pharmacological Test Example 1 Rat Test 1 1. TestMethod

Diabetes mellitus was induced in male Sprague Dawley rats (8-week-old)weighing about 250 g by injecting streptozotocin (STZ manufactured bySigma) intravenously into their tail at the dose of 60 mg/kg. One weekafter the treatment with STZ, serum glucose was measured, and rats withat least 300 mg/dl glucose were then used in the experiment as diabeticrats. The set groups were the following 3 groups, and after 2 weeksafter the treatment with STZ, 5% gum arabic solution or SNK-860 solutionwas orally administered once a day.

(1) Normal control group (5 rats): Given 5% gum arabic solution in aratio of 5 ml/kg.(2) Diabetic control group (7 rats): Given 5% gum arabic solution in aratio of 5 ml/kg.(3) Diabetic group given 32 mg/kg SNK-860 (4 rats): Given a suspensionof SNK-860 (32 mg/5 ml) in 5% gum arabic solution in a ratio of 5 ml/kg.

After administration for 2 weeks, intraocular ischemia was caused by thetreatment described below. After the treatment was finished, the animalswere maintained as usual for 2 days, and thereafter, the eyeballs wereexcised and histologically evaluated. Administration of thepharmacological agent was also conducted for a period (2 days) ofreperfusion after ischemic treatment.

Retinal Ischemia by Increasing the Intraocular Pressure

A drip infusion set (Terufusion Drip Infusion Set manufactured byTerumo) was connected to a bottle containing an intraocular perfusionsolution (Opeguard MA manufactured by Senjyu Seiyaku), and an extensiontube (Terumo) to which a three-way stopcock had been attached wasconnected thereto. A needle (30 G×½, manufactured by Nippon BectonDickinton) was fitted to the end of the tube. The bottle containing anintraocular perfusion solution was fixed to a certain height with astand. The rats were anesthetized by administering sodium pentobarbital(Somunopentyl manufactured by Schering-Plough Animal Health)intraperitoneally in a ratio of 50 mg/kg, and then a mydriatic (Mydrin Pmanufactured by Santen Pharmaceutical) and a local anesthetic (Benoxyleye drop 0.4%, Santen Pharmaceutical) were dropped onto the right eye.The anesthetic was additionally administered when necessary. Thereafter,a needle was stuck into an anterior chamber of the rat right eye and theintraocular pressure load was performed by manipulating the three-waystopcock (the intraocular pressure was increased to 130 mmHg or more for60 minutes). Because the ocular fundus in the Sprague Dawley rat turnsfrom red to white by stopping the retinal blood stream by increasing theintraocular pressure, achievement of retinal ischemia can be easilyobserved. After the intraocular pressure was increased for thepredetermined time, the needle was removed to relieve the intraocularpressure to allow reperfusion, and an antibacterial eye drop (tariviteye ointment manufactured by Santen Pharmaceutical) was applied onto theright eye.

Histological Evaluation

Two days after the ischemia treatment (two days after the reperfusion),the rat left and right eyeballs were excised under anesthesia withether. The excised eyeballs were placed in an ice-cold fixing solution(phosphate buffer solution containing 3% glutaraldehyde) and fixedtherein for 2 days. Thereafter, the eyeballs were washed for 1 day witha phosphate buffer solution. The eyeballs were embedded in a usualmanner into paraffin to prepare a transverse section containing a bundleof optic nerves. The section was stained with hematoxylin-eosin. Thehistological evaluation was conducted by each of two (2) visual fieldsin left and right side (4 visual fields/rat) in the vicinity of thebundle of optic nerves, from an optical microscope to an image analyzer(IPAP-WIN, Sumika Techno Service).

In each of the resulting retinal images, the thickness of the visualcell layer was measured. The degree of edema was expressed in percentageby dividing the thickness of the visual cell layer of theischemic/re-perfused eyeball (right eye) by the thickness of the visualcell layer of the untreated eyeball (left eye) in the same individual.As an indicator of retinal cell functions, nuclei in the inner retinallayer (ganglion cell layer) were counted, and the degree of loss ofnuclei was evaluated relative to the ratio of the number of nucleioccurring per unit area.

2. Results and Discussion

The effect of SNK-860 on edema is shown in FIG. 1. The thickness of thevisual cell layer after ischemia/reperfusion in the rats in the normalcontrol group was reduced as compared with that of the untreated eye. Onthe other hand, the rats in the diabetic control group showed anincrease in the visual cell layer by ischemia/reperfusion, and formationof edema was confirmed (p<0.05). In the diabetic group given 32 mg/kgSNK-860, the thickness was almost the same as that of the normal controlgroup, and no edema was observed.

Next, loss of nuclei from ganglion cells is described. As a result ofexamination of the degree of loss of nuclei from cells, no loss ofnuclei was recognized in 5 rats in the normal control group. In thediabetic control group, evident loss of nuclei occurred in 3 of 7 rats,among which 2 rats showed loss of 50% or more nuclei. In the diabeticgroup given 32 mg/kg SNK-860, loss of nuclei was not observed in all 4rats.

These results reveal that SNK-860 inhibits edema formation underdiabetes in a visual cell layer and also prevents disturbances infunctions of retinal cells.

Efficacy Pharmacological Test Example 2 Rat Test 2 1. Test Method

The test was carried out in accordance with Efficacy PharmacologicalTest Example 1. The set groups were the following 4 groups, and from 2weeks after the treatment with STZ, 5% gum arabic solution or SNK-860solution was orally administered once a day.

(1) Normal control group (10 rats): Given 5% gum arabic solution in aratio of 5 ml/kg.(2) Diabetic control group (9 rats): Given 5% gum arabic solution in aratio of 5 ml/kg.(3) Diabetic group given 2 mg/kg SNK-860 (10 rats): Given a suspensionof SNK-860 (2 mg/5 ml) in 5% gum arabic solution in a ratio of 5 ml/kg.(4) Diabetic group given 32 mg/kg SNK-860 (9 rats): Given a suspensionof SNK-860 (32 mg/5 ml) in 5% gum arabic solution in a ratio of 5 ml/kg.

Retinal ischemia produced by increasing the intraocular pressure was inaccordance with Efficacy Pharmaceutical Test Example 1. Histologicalevaluation was also in accordance with Efficacy Pharmaceutical TestExample 1.

2. Results and Discussion

The effect of SNK-860 on edema is shown in FIG. 2. The thickness of thevisual cell layer after ischemia/reperfusion in the rats in the normalcontrol group was reduced as compared with that of the untreated eye. Onthe other hand, the rats in the diabetic control group showed anincrease in the visual cell layer by ischemia/reperfusion, and formationof edema was confirmed (p<0.05). In the diabetic group given 2 mg/kgSNK-860, no inhibitory action on edema was observed, but in the diabeticgroup given 32 mg/kg SNK-860, the thickness of the visual cell layer waskept in the same value as in the normal control group, and an evidentinhibitory action on edema was observed. These results indicate thatedema formation under diabetes in a visual cell layer is inhibited byadministration of a high dose of SNK-860.

Efficacy Pharmacological Test Example 3 Monkey (Macaca fascicularis)Test 1. Method

Diabetes mellitus was induced in male monkeys (Macaca fascicularis)(3-year-old) weighing about 2.1 to 2.4 kg by intravenously injecting STZinto their foreleg vein at the dose of 80 mg/kg. Two days after thetreatment with STZ, blood glucose level was measured, and monkeys withat least 200 mg/dl glucose were then used in the experiment as diabeticmonkeys. Insulin was administered subcutaneously once or twice per dayinto monkeys showing a blood glucose level of 300 mg/dl. The set groupswere the following 3 groups, and from 2 weeks after the treatment withSTZ, 5% gum arabic solution or SNK-860 solution was orally administeredonce a day.

(1) Normal control group (4 monkeys): Given 5% gum arabic solution in aratio of 5 ml/kg.(2) Diabetic control group (6 monkeys): Given 5% gum arabic solution ina ratio of 5 ml/kg.(3) Diabetic group given 32 mg/kg SNK-860 (4 monkeys): Given asuspension of SNK-860 (32 mg/5 ml) in 5% gum arabic solution in a ratioof 5 ml/kg.

After administration for 2 weeks, intraocular ischemic treatment wascarried out as described below, and after the treatment was finished,the animals were maintained as usual for 7 days. Before the ischemictreatment and 7 days after treatment, the thickness and volume of themacular central fovea (in the diameter range of 1 mm from the center ofthe macula lutea) were measured by an OCT scanner (Stratus OCT, CarlZeiss). Administration of the pharmacological agent was also conductedfor the period (7 days) of reperfusion after the ischemic treatment.

Retinal ischemia produced by increasing intraocular pressure was inaccordance with Efficacy Pharmaceutical Test Example 1. However, thesize of the needle used was 25 G×½ (Terumo). After a mydriatic (Mydrin Pmanufactured by Santen Pharmaceutical) was dropped onto the right eye,the monkey was anesthetized by intramuscularly administering ketaral(Sankyo Life Tech). Subsequently, a local anesthetic (Benoxyl eye drop0.4%) was dropped onto the eye, and the monkey was prevented fromblinking with an eyelid speculum. Anesthesia with ketaral wasadditionally carried out when necessary.

The thickness and volume of the macular central fovea were measured inthe following manner. After a mydriatic (Mydrin P) was dropped onto theright eye of the monkey to dilate the pupil of the eye sufficiently, themonkey was anesthetized by intramuscularly administering Ketaral.Thereafter, the monkey was allowed to sit on a monkey chair and the headwas fixed. The inside of the eye was observed with an OCT scanner toidentify the macula lutea, followed by scanning. On the basis of theresulting cross-sectional macular image, the thickness and volume of themacular central fovea were analyzed.

TABLE 1 Average macula lutea Average macula lutea thickness (μm) volume(mm³) Number Before 7 days after Before 7 days after Group of monkeysischemia ischemia ischemia ischemia Normal 4 174 ± 8 175 ± 11 0.137 ±0.006 0.138 ± 0.009 Diabetes 6 177 ± 6 191 ± 5** 0.139 ± 0.005 0.149 ±0.004** mellitus Diabetes 4 157 ± 6 158 ± 2 0.123 ± 0.005 0.124 ± 0.001mellitus given 860 **P < 0.01 vs. “value before ischemia”.

2. Results

The results are shown in Table 1 and FIG. 3. In the normal controlgroup, formation of edema was not observed, and the thickness and volume(average) of the macular central fovea after ischemia and reperfusionwere the same before the treatment and 7 days after the treatment. Inthe diabetic control group, on the other hand, an increase in thethickness and volume of the macular central fovea was observed 7 daysafter the treatment, and formation of edema was confirmed (p<0.01). Thischange was significantly increased as compared with that of the normalcontrol group (p<0.05). In the diabetic group given 32 mg/kg SNK-860,formation of edema or its change was not observed similarly to thenormal control group. These results show that SNK-860 inhibits edemaformation under diabetes in the macular central fovea.

Efficacy Pharmacological Test Example 4 Clinical Results 1. Method

Among patients with diabetic maculopathy, 10 patients with diabeticmacular edema having a retinal thickening or a hard exudates in aposterior pole of the retina were subjects. SNK-860 was orallyadministered in a dose of 30 mg (2 tablets each containing 15 mgSNK-860) once a day before breakfast for 8 weeks. During this testperiod, simultaneous use of eparlestat, intravitreal injection andsub-Tenon injection of an adrenal cortical hormone, and photocoagulationand vitrectomy were prohibited. Basic therapy of diabetes mellitus wascarried out so as to give good blood glucose control throughout the testperiod.

Evaluation was carried out in terms of the thickness of the macularcentral fovea (in the diameter range of 1 mm from the center of maculalutea) and the thickness at the center of the central fovea measured byoptical coherence tomography (OCT, Carl Zeiss), as well as correctedvisual acuity (Log MAR).

Log MAR (Log Minimum Angle of Resolution) is one kind of logarithmicvisual acuity, which is visual acuity expressed in logarithmic minimumangle of resolution. Decimal visual acuity 1.0 used frequently in Japanis 0.0 in terms of Log MAR, and decimal visual acuity 0.1 is 1.0 in LogMAR. A log MAR visual acuity of 0.1 to 0.5 corresponds to a decimalvisual acuity of 0.8 to 0.32.

TABLE 2 Macula lutea thickness (μm) and corrected visual acuity (LogMAR) (mean ± standard deviation) When initiated Week 8 P value Center ofcentral fovea 323.1 ± 111.4 298.7 ± 90.6 0.0808 Central fovea (diameter:1 mm) 324.3 ± 87.7  300.4 ± 74.4 0.0493 Corrected visual acuity 0.30 ±0.22  0.24 ± 0.20 0.0917

TABLE 3 Corrected visual acuity (eye number) 2-stage 1-stage 1-stageimprovement improvement Unchanged deterioration 3 2 6 1

2. Results

12 eyes in the 10 cases were evaluated. When the test was initiated, thethickness of the macular central fovea (in the diameter range of 1 mm)was 324.3 μm on average, and the thickness at the center of the centralfovea was 323.1 μm on average. After 8 weeks, these were reduced 300.4μm and 298.7 μm respectively (Table 2, FIG. 4). A change in thethickness of macula lutea in the individual evaluated eye is shown inFIG. 5. These results show that the thickness of the macula lutea or theportion corresponding to the macula lutea in the model animal was alsoconfirmed similarly in humans.

Out of the 12 eyes, 2-stage development with respect to corrected visualacuity was recognized in 3 eyes, 1-stage development in 2 eyes, anddeterioration in only 1 eye (Table 3). The corrected visual acuity (LogMAR) on average was improved from 0.30 to 0.24 (FIG. 6). It was thusrevealed that SNK-860 has a visual acuity-improving action important intherapy of maculopathy.

Diabetic maculopathy according to conventional findings is a graduallyworsening disease that is considered difficult to treat. In contrast,the results of the present examples indicate that SNK-860 is effectivefor diabetic maculopathy. With respect to safety, no particularlyproblematic side effects were recognized.

1. A method for treating diabetic macular edema comprising administering to a subject in need thereof an effective amount of a compound represented by the following general formula:

wherein X represents a halogen or a hydrogen atom, and R¹ and R² concurrently or differently represent a hydrogen atom or a C1 to C6 alkyl group.
 2. The method for treating diabetic macular edema according to claim 1, wherein the compound is (2S,4S)-6-fluoro-2′,5′-dioxospiro[chroman-4,4′-imidazolidine]-2-carboxamide.
 3. The method for treating diabetic macular edema according to claim 1, wherein a condition being treated is diffuse macular edema.
 4. The method for treating diabetic macular edema according to claim 1, wherein the method causes an improvement in visual acuity or inhibition of a deterioration of visual acuity in a subject having diabetic macular edema.
 5. A method for improving visual acuity or inhibiting a deterioration of visual acuity in a subject having diabetic macular edema comprising administering to the subject in need thereof an effective amount of a compound represented by the following general formula:

wherein X represents a halogen or a hydrogen atom, and R¹ and R² concurrently or differently represent a hydrogen atom or a C1 to C6 alkyl group.
 6. The method for improving visual acuity or inhibiting a deterioration of visual acuity according to claim 5, wherein the compound is (2S,4S)-6-fluoro-2′,5′-dioxospiro[chroman-4,4′-imidazolidine]-2-carboxamide. 